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Status Reports

The blue lines superimposed over a Google Earth image of Iceland shows the tracks flown by NASA’s Gulfstream III science research aircraft during one of the Arctic Ice Radar Mission flights flown during the second week of June 2009. (NASA image / Roger Chao)› View larger image
By June 8, NASA’s UAVSAR team had completed all the objectives of the Arctic Ice Radar Mission in Greenland and flew to Keflavik International Airport to measure the topography and 3D surface velocities of the temperate ice caps of Iceland.

Between June 10 and June 14, NASA’s Gulfstream III science research aircraft flew five repeat data flights over Iceland. Using the onboard L-band radar enclosed in the UAVSAR pod mounted on the aircraft’s belly, Jet Propulsion Laboratory engineers collected 59 data lines and recorded approximately 1.28 terabytes of data during the five-day mission. The data will provide important mission design constraints for future remote sensing satellites by testing how temperate ice behaves over different time intervals when measured by an interferometric L-band radar.

Using these data, scientists would also be able to measure the speed, direction and topographic height of ice caps whose sub-glacial bedrock topography is already mapped – thereby providing critical information that can be used to improve models of glacier mechanics.

After completing all the science objectives on June 14, the Gulfstream III flew back to Bangor, Maine, to continue its remaining Everglades, Aanstoos site and Gulf Coast missions.

L-band polarmetric image of the Kangerlugssuaq ice fjord, centered at 68 degrees 38 minutes North, 33 degrees 03 minutes West. This false color 17 x 30 km SAR image is a composite of three polarizations with HH polarization colored red, HV colored green, and VV colored blue. (SAR image / Ron Muellerschoen)> Full resolution photo
After an overnight stay in Bangor, Maine, the NASA Gulfstream III carrying the polarmetric L-band radar built by NASA's Jet Propulsion Laboratory,or JPL, flew back to Greenland May 20. During transit back to Thule, JPL engineers recorded a multi-scan data line over the Atlantic Ocean. Data from this line will allow scientists to better understand the structure of ocean wave fields. Knowledge of the two-dimensional wave spectra of these fields is important for such practical applications as wave forecasting for trans-oceanic ship routing, and for designing offshore installations.

Two crossing data lines were additionally collected near the Kangerlugssuaq fjord on the east coast of Greenland. This fjord is a major outlet of the Kangerlugssuaq glacier as it flows south of Watkins Mountain Range and into the Kartografvig Bay. These crossing flight lines were to be repeated two weeks later to study the evolution and deformation of this important glacier stream.

On May 21 and May 22, science objectives took the NASA Gulfstream III to Northern Greenland and back up to Alert, Canada, at 82.5 degrees north latitude and into the western interior of Greenland. JPL engineers collected seven data lines May 21 and recorded more than 1.7 hours of radar echoes. On May 22, the aircraft repeated some of the previous day's data lines twice. Scientists not only want to study how the glacier evolves on time spans of weeks and days, but also how it evolves on time scales as short as a few hours. Airborne remote sensing allows scientists to have this flexibility on when they can schedule observation times as they look for changes over different time scales.

From the four L-band data flights flown during the week of May 15 through May 22, JPL engineers collected 23 data lines and recorded 938 gigabytes of data. Since NASA's Gulfstream III deployed May 1, 1,800 gigabytes of data have been accumulated. These data will allow scientists to understand how Arctic glaciers are changing, and how to design the next generation of instruments for future remote sensing satellites.

Ron Muellerschoen
NASA Jet Propulsion Laboratory

Removing the Ka Pod - 06.04.09

NASA technician Gary Carlson removes the Ka-band waveguide before exchanging the Ka-band radar pod for the L-band pod mounted underneath NASA’s G-III research aircraft. (NASA Photo / Chris Miller)
The NASA Gulfstream III carries its radar instruments in an exterior pod that hangs down from the aircraft. NASA’s Jet Propulsion Laboratory, or JPL, has built two radar instruments that are housed in separate pods.

For deployment to Greenland, the aircraft carried the Ka-band cross-track interferometer radar instrument. This instrument is capable of producing detailed elevation maps of the observed terrain in the swath. With this Ka-band instrument, the JPL and Dryden team collected 75 data lines and accumulated 862 gigabytes of data. This data has been dispatched back to JPL for engineers and scientists to dissect and explore the topography and changes of Greenland’s massive ice glaciers and outlet fjords.

The next part of the deployment involved the fully polarmetric L-band instrument housed in the second pod. This pod arrived via a C-17 transport on May 14. Within hours of its arrival, the Dryden crew quickly swapped out the Ka-band pod for the L-band pod.

We flew the first L-band mission May 15. This would be the first of many repeat pass flights over the interior of Greenland’s glaciers. By comparing radar images from repeated flights over the same terrain, changes as small as 1 millimeter and as large as half the wavelength of the L-band instrument, or about 10 centimeters, can be detected. While the Ka-band instrument was designed to compute cross-track interferometric topography of the terrain, the L-band instrument was designed to compute repeat-pass interferometric deformation between observation times.

Our first L-band flight May 15 took us north to Alert, Canada, at 82.5 degrees north latitude and into the western interior of Greenland. We collected six data lines and accumulated 258 gigabytes of data. In order to observe more with the L-band instrument, the data window of the radar, or observation time per radar echo, was increased to 150 microseconds. This is 2.5 times larger than the Ka-band data window. As a result, the data volume we must now store, transport, and analyze increased 2.5 times.

On the return to Thule, power failed on some of the auxiliary circuits of the aircraft. Upon landing the Dryden crew discovered a power inverter had failed and had to be replaced. Quick work by the crew and mission manager located a spare part. However, obtaining the part and fixing the aircraft in a timely manner required us to return to the United States. On May 19 the Gulfstream III flew to Bangor, Maine, briefly to repair the failed power circuit. On our return trip to Thule May 20, we flew over the Eastern portion of Greenland and performed the first over flights for a repeat pass deformation study of the Kangerlugssuaq glacier.

These two radar images taken on May 6 and May 12 of Greenland's Jacobshaven glacier from the Ka-band radar carried on NASA's G-III research aircraft show evidence of ice recession or "calving" of almost a kilometer during the six-day period. (NASA radar image)

On Monday, May 11, scientists aboard NASA's Gulfstream III research aircraft returned to Jakobshaven glacier with the objective of repeating the data lines recorded by the Ka-band radar during flights on May 5 and 6. Scientists want to obtain a complete three-dimension map of the Jakobshaven glacier, and more important, how it has evolved over a relatively short period of time.

Jakobshaven is one of Greenland’s outlet glaciers. It generates large quantities of icebergs and releases massive amounts of fresh water into the Atlantic Ocean. This influx raises sea level, and has the potential to change ocean circulation patterns due to lowering the salinity of the ocean’s water. Jakobshaven drains as much 6.5 percent of Greenland ice-sheet melt-water and produces nearly 10 percent of all the Greenland’s icebergs. The calving front, a wall of ice that separates the inland glacier ice from the fjord, has been closely monitored with records going back to 1851. This front has historically receded gradually, but within the last decade there has been a substantial retreat of this ice wall away from its ocean outlet.

On May 11, scientists collected 11 data lines and on May 12 we collected an amazing 15 data lines before we hit what the pilots call “bingo” – a term used when they have just enough fuel to safely return to base and if necessary divert to another airstrip in case of bad weather. On both these days the air at flight altitude was 20 degrees colder than expected, which resulted in denser air. The denser air allowed the airplane to be more efficient on fuel, so we were able to linger over the targets longer than during the previous missions.

Back in Thule, we post-processed the Ka-band radar data for both the May 5 and 6 mapping and remapping from May 11 and 12. From the data we observed a dramatic evolution of the Jakobshaven calving front. In the six days that passed between when we first collected data from the site, the calving wall moved inland over 1 kilometers. Additionally, icebergs in the frozen fjord could be seen downstream as far as 4.8 kilometers. We suspect this is only the beginning of the many surprises we will see once we analyze the data.

With clear skies and light winds during the first week of their mission, scientists participating in NASA's Arctic ice radar measurement and mapping mission over Greenland and Iceland pushed ahead with several flights during the week of May 3 to 9.

"At some point in the schedule, the weather may turn bad and force a no-fly day," commented project engineer Ron Muellerschoen of NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Therefore getting ahead of schedule now may prove to be judicious in the coming weeks."

On May 7, scientists aboard NASA's Gulfstream-III research aircraft captured data lines that were missed during a previous flight over the Jakobshaven glacier on May 6. They then headed further south towards Søndre Strømfjord, which is Danish for Kangerlussuaq. Kangerlussuaq was home to an American military base during the Cold War, but now is a small town that is served by Greenland Air. It also was home to the P3 Orion aircraft from NASA’s Wallops Flight Facility, Wallops Island, VA., when it was deployed to Greenland recently with the Airborne Topographic Mapper.

Using the UAVSAR and Ka-band radars mounted on the aircraft's underbelly, scientists collected data while flying two precision north-south lines over the Jakobshaven glacier and then an west-to-east line starting at the ocean and following the glacier flow as it rises to 1,400 meters above sea level, Muellerschoen reported. The flight then turned south and accumulated four data lines over the Smith Study area near Kangerlussuaq. Scientists on the ground in the study area gathered data on snow density, granularity and wetness that will be compared with the radar data. The returned signal, along with the data gathered on the ground, will provide valuable calibration information of the backscatter, or returned power in the echoes, for future Arctic glacier Ka-band radar investigations.

The team flew six missions in seven days, logging nearly 35 flying hours during the week, Muellerschoen noted. Mission scientists collected 48 data lines and 621 gigabytes of data with JPL’s Ka-Band cross-track interferometric radar. During the week of May 10-16, the the Ka-Band radar was scheduled to be replaced with an L-Band radar. This instrument will allow team members to acquire fully polarmetric data as they begin the repeat pass deformation study portion of Greenland and Iceland glaciers.

After preliminary processing, Ka-band data acquired on May 5, 2009 shows the boundary between the land and flow of the Jakobshavn glacier. (NASA SAR Image / Ron Muellerschoen) Cross-track Interferometry – How JPL's Ka-band Radar Works - 05.13.09

The objectives for the two flights on May 5th and May 6th was to perform a systematic mapping of the Jakobshavn glacier. High-resolution topography will allow scientists to understand the driving stresses and resulting strains of the fastest-moving glacier in Greenland.

The Ka-band instrument is equipped with two antennas separated by a half meter. The bottom antenna transmits microwave energy that is reflected from the ground and detected by both the bottom and the top antennas. These two “eyes” of the Ka-band instrument provides the depth perception that you cannot get with just one antenna.

Technically speaking there is a component of the baseline between these two antennas that is perpendicular to the line-of-sight such that they don’t record the same received signal. This is called cross-track interferometry. The observed phase difference of the returned echos between the top and bottom antennas gives the Ka-band instrument depth perception. From this, and a little bit of math and a whole lot of computing power, we can obtain the topography of the image observed in the radar’s swath.

On May 5th we acquired nine data lines and 95 gigabytes of data from the radar. On May 6th we acquired 11 data lines and 120 gigabytes of data. On Thursday, we will fly over the Swiss Camp near the Jakobshavn glacier where we will again have ground truth collected by the Greenland Climate Network.

Later this month the UAVSAR and Ka-band instrument will revisit and again systematically remap the Jakobshavn glacier. Scientists will then be able to compare the two topographies collected and accurately determine the movements of the glacier between the two observation times.

Corner reflector is installed at Summit Camp to support UAVSAR Ka-band calibration. (Summit Camps Photo / Lana Cohen)
After a light snowfall on Monday, May 4, skies cleared and NASA's G-III research aircraft took to the skies, flying over the summit of Greenland, nearly 11,000 feet (3,250 meters) in altitude, and back down to sea level at Jakobshavn glacier on the west coast of Greenland.

This flight had two objectives -- the first to measure how deep the Ka-band microwave radiation will penetrate into the ice of the glaciers, the second to calibrate the radar returns.

To accomplish that, scientist used three coordinated assets. One asset is the Airborne Topographic Mapper (ATM) flown on NASA's P3 Orion aircraft out of NASA's Wallops Flight Facility, Wallops Island, Va. The ATM uses lidar to measure the precise height of the glacier directly below the aircraft’s path. The UAVSAR Ka-band instrument was precisely guided to image the same path. The amount of penetration of the Ka-band microwave radiation will then be the difference between these two measurements. Computer models predicted there may be as much as one foot (30 cm) of penetration into dry snow.

To calibrate the radar, scientists from the Greenland Climate Network, or GNC, placed corner reflectors on the glacier’s surface at the summit and also down at the Jakobshavn glacier. These three-foot (1m) trihedral structures appear to the airborne radar as perfect reflectors of the transmitted microwave energy. Once the apex of the reflectors is measured to within a few centimeters by GPS, their positions allow JPL engineers to fine-tune the airborne radar and calibrate electronic delays in the signal.

Also, knowing the orientation and elevation or tilt of the corner reflectors relative to the microwave radiation allows the engineers to compute a model for the amount of energy they expect to see returned from these ground reflectors. This model can then be compared to the amount of energy actually measured at the aircraft. The difference between the modeled returned and the measured returned could then be used to calibrate the electronics of the Ka-band radar.

The third asset used by JPL scientists was the assistance of the GNC to provide ground truth of the imaging sites. The GNC measured snow wetness, snowfall, densification of the ice, and snow granularity. Computer models suggest that penetration of Ka-band microwave radiation into ice and snow drops off as a function of snow wetness. Experimental data was gathered to calibrate these computer models.

On this first mission over Greenland, the NASA JPL/Dryden project team acquired 143 gigabytes of data during nine data collection flight lines. Later this week we plan to return to Jakobshavn glacier for a systematic two-day mapping of its terrain.

Ron Muellerschoen
Jet Propulsion Laboratory

Arctic Ice Radar Surveys Now Under Way in Greenland, Iceland - 05.05.09

JPL scientist Tim Miller acquires data over North America’s wetlands on NASA Dryden’s twin-jet Gulfstream III equipped for airborne radar investigation of the Greenland and Iceland glaciers. (NASA photo / Chung-Lun “Ernie” Chuang)
After a two-day ferry flight from NASA's Dryden Flight Research Center in Southern California, a team of scientists and pilots aboard NASA's Gulfstream-III environmental research aircraft have begun flying missions intended to monitor the flows and map Arctic ice fields and glaciers in Greenland and Iceland.

This mission marks the first time that two new Ka and L-Band synthetic aperture radars, or SAR, both developed by NASA's Jet Propulsion Laboratory, or JPL, have been deployed in an operational science mission.

The G-III arrived in Thule, Greenland last Saturday after a two-day ferry flight from Edwards Air Force Base. On the ferry flight, scientists aboard the modified business jet collected data to validate the operation of the two advanced radar systems on the aircraft over both North American prairies and wetlands and sea ice.

From an altitude of 41,000 ft, scientists collected eight lines of Ka-band data lines en-route to their first overnight stop in Grand Forks, North Dakota. The 5.4-hour flight acquired data along the upper Missouri River, Devil’s Lake North Dakota, the Red River bordering Minnesota and North Dakota, and the “Big Bog” wetlands of Minnesota.

According to JPL mission scientist Ron Muellerschoen, the science objectives for these data collections was not so much topography, which will be a high priority objective over Greenland, but rather to characterize backscatter statistics of the radar when it is being transmitted and received at near vertical angles. Typical SAR viewing geometries have the radar pulsing microwave energy at an angle relative to the vertical so as to acquire reflections from the ground over a large extended swath. To accomplish the near-vertical transmissions and returns, NASA Dryden pilots Dick Ewers and Troy Asher banked or "crabbed" the airplane as much as 10 degrees so as to point the radar towards the vertical as much as possible while still flying in a straight line.

NASA Dryden's Gulfstream III research aircraft on the ramp at Thule, Greenland after a two-segment ferry flight from Edwards AFB in Southern California. The UAVSAR radar pod hangs from the aircraft's belly. (NASA photo / Ron Muellerschoen)
On approach to Thule near the end of the ferry flight's second segment, scientists aboard the G-III collected one additional line of data from a near-vertical angle, this time over sea ice. The data collected almost directly below the aircraft matched the viewing angles of the Surface Water and Ocean Topology (SWOT) Earth-observing satellite being developed at JPL. Muellerschoen said the characteristics of the data will provide valuable information to SWOT scientists and engineers on how to best design the instrument for that spacecraft.

Real-time decisions were made on the flight to open and close the radar’s observation window so that nearly one-third of the radar pulse length transmitted remained “in the air” and not reflected from the surface, while the remaining two-thirds of the pulse length was returned as reflected energy.

Muellerschoen said scientists observed very dynamic echoes or radar returns over the sea ice as they monitored them from the aircraft, while a few moments later the transmitted microwave energy would be absorbed by the sea with very little signal being reflected over the open water.
After arrival in Thule, the mission's first airborne data campaign to investigate Greenland’s glaciers was scheduled to begin this week.

NASA's Gulfstream-III research testbed lifts off from Edwards AFB on a checkout test flight with the UAV synthetic aperture radar pod under its belly. (NASA photo)
A team of NASA scientists are conducting an airborne campaign this spring to better understand how Arctic ice is changing and assess the impacts of climate change. During the seven-week Uninhabited Aerial Vehicle Synthetic Aperture Radar field campaign to Greenland and Iceland, scientists will use two new ice-penetrating radars flying aboard a modified Gulfstream III aircraft operated by NASA's Dryden Flight Research Center.

Data collected during this mission will provide new insights into our understanding of the flow of glaciers and ice streams while also serving as a test bed for future satellite missions. Scott Hensley of NASA's Jet Propulsion Laboratory in La Canada-Flintridge, Calif., leads the campaign.

The synthetic aperture radar airborne campaign being flown on NASA's Gulfstream III aircraft is a continuation of environmental science missions conducted during the International Polar Year. The two-year International Polar Year focused science and education activities on Earth's remote polar regions and their connections to the rest of the Earth system.

The International Polar Year prompted many research projects and innovative public outreach programs. Although the International Polar Year officially came to a close in February, NASA is continuing to push the frontiers of polar science from space, the air and the surface of ice.